Apparatus has previously been proposed to indicate rotation of elements shielded from direct view by a user. U.S. Pat. No. 4,245,370 to Baker discloses such a device. In this device, a magnet is carried by a rotating beater brush housed within the rug cleaning nozzle of a domestic vacuum cleaner. The magnet revolves about the axis of rotation of the beater brush as it rotates. A Hall effect sensor located adjacent to the path of the revolving magnet provides a pulse signal, the frequency of which is indicative of the rotational speed of the beater brush. This sensor signal is supplied to a relatively complex, externally powered control circuit that performs various functions, including illumination of a selected one of a plurality of user-viewable light emitting diodes which indicate the rotational status of the beater brush.
The copending application of John F. L. England, Ser. No. 806,699, filed Dec. 9, 1985, entitled "Self-Powered Rotation Indicator," and incorporated herein by reference in its entirety, discloses a rotation indicator which may be used in conjunction with a rotating machine element which is normally shielded from direct view of the user. That invention may be utilized in a domestic vacuum cleaner nozzle, and discloses a luminous indicator device which is electrically powered solely be energy derived from the rotating element which the indicator is monitoring. Such application discloses a rotating permanent magnet cooperating with a coil of wire to generate an alternating voltage in the coil which is supplied to a light emitting diode lamp viewable by the user of the vacuum cleaner through an aperture in the nozzle of the vacuum cleaner.
The prior art Baker device functions to provide a visual indication of the rotational status of a rug beater brush, yet its complexity makes it unattractive from a cost and reliability standpoint, it being recognized that the domestic appliance business is highly competitive. The prior art device disclosed in the above-mentioned copending application provides an indicator unit with only a small number of parts, yet it has been determined that the large number of turns of fine wire on the coil, the connection of the coil to the lamp, and the difficulty of positioning the parts caused the manufacturing cost to be excessive.